No
yes weasels live in grasslands
No, there are no weasels in Ireland. There are stoats, which some people mistake for weasels, but there are no actual weasels in Ireland.
does least weasels travel in groups
yes
Anywhere
Long & Short-Hair weasels The Least Weasel
yes
Weasels live in nooks and crannies, holes on trees and under rocks.
No. Weasels are neither native to Australia, nor have they been introduced to Australia. Weasels have been introduced to New Zealand, but New Zealand is not part of Australia. It is a totally separate country.
Yes, weasels do live in sets.
Typically there are about 200 penguins that will live together. There is however no limit to how many penguins will live together.